Fluorescent proteins have been facilitating live cell imaging, and thus various structures in cells and various functions thereof have been clarified. In recent years, a super-resolution method using fluorescent proteins whose fluorescence can be reversibly photo-switched (reversibly photo-switchable fluorescent protein, RSFP) has been developed, and thus imaging can be performed beyond the diffraction limit of an optical microscope. Examples of the RSFPs include 1) a negative photo-switchable type (e.g., Dronpa (Patent Document 1) and rsEGFP) that switches from a non-fluorescent state to a fluorescent state by being irradiated with light having a specific wavelength that does not cause fluorescence excitation and switches from a fluorescent state to a non-fluorescent state by being irradiated with light for fluorescence excitation; 2) a positive photo-switchable type (e.g., Padron (Non-Patent Document 1)) that switches from a non-fluorescent state to a fluorescent state by being irradiated with light for fluorescence excitation and switches from a fluorescent state to a non-fluorescent state by being irradiated with light having a specific wavelength that does not cause fluorescence excitation; and 3) a type (e.g., Dreiklang) in which wavelengths for the switching on/off of the fluorescence and a fluorescence excitation wavelength are entirely independent of each other.